JPS6340135B2 - - Google Patents

Abstract

Fuel cell with improved and stabilized electrode performance having at least one gas diffusion electrode, where the gas diffusion electrode comprises an electronconductive, gas-permeable substrate and an electrode catalyst uniformly distributed on the substrate, the electrode catalyst comprising colonies each consisting of not more than 20 primary particles of noble metal each having a size of 10-30 A and being uniformly distributed and deposited on carrier powder.

Description

[Detailed description of the invention]

The present invention relates to a fuel cell electrode catalyst capable of uniformly dispersing and depositing noble metal element particles on a carrier to form an electrode having a solid-liquid-gas three-phase interface, and a method for producing the same. In order to produce electrodes with good performance in fuel cells, it is necessary to increase the activity of the electrode catalyst that forms the basis of the electrode, and to create a state that facilitates the formation of a solid-liquid-gas three-phase interface during electrode formation. is necessary. Generally, noble metal elements (hereinafter simply referred to as noble metals)
The activity of the catalyst is increased by micronizing the noble metal particles and uniformly dispersing them on the support. Many methods for preparing noble metal catalysts have been known. Generally, for example, activated carbon or carbon black is impregnated with a chloroplatinic acid solution, and this is wet-reduced using chemicals or dry-reduced using reducing gas. be. More recently, Henry J. Petrou has proposed depositing fine platinum particles on a support by forming a platinum sulfite complex followed by oxidation treatment. (Unexamined Japanese Patent Publication No. 51-88478
In addition, Vinoud Monaral Dialan also reported that 50% of the chloroplatinic acid solution was deposited on a carbon support using sodium dithionate and hydrogen peroxide.
It is disclosed that it is possible to deposit platinum particles of Å or less. (Refer to Japanese Unexamined Patent Publication No. 54-92588.) On the other hand, there is a method for preparing a dispersion of colloid and platinum particles using polyvinyl alcohol (hereinafter abbreviated as PVA) as a protective colloid.
Report by Nord et al. [J.Am.Chem.Soc., 63 , 2745
(1941)], and more recently, a report by Nakamichi and Hirai [see obverse, 17 , (4), 279-289 (1979)].
There is. In addition, the present inventors have found that by using this protective colloid method, fine precious metal particles can be uniformly dispersed and supported on a carbon carrier by changing the surface condition of the carrier and the type and amount of the hydrophilic polymer. It was confirmed. However, despite the high activity of the electrocatalyst itself, the performance of the electrode using this method was found to be greatly affected by the process of controlling the three-phase interface of the electrode, as described above. did. The present invention has been made from this perspective, and its purpose is to create an electrode with stable performance that has a solid-liquid-gas three-phase interface by making noble metal particles fine and uniformly dispersing them on a carrier. An object of the present invention is to provide a fuel cell electrode catalyst capable of forming a fuel cell electrode catalyst and a method for producing the same. To summarize the present invention, the fuel cell electrode catalyst of the present invention (first invention) consists of noble metal element particles, carbon-based powder, and fluorinated graphite particles, and the noble metal element particles are made of fluorinated graphite particles. The method for producing a fuel cell electrode catalyst of the present invention (second invention) is characterized in that it is supported on a carbon-based powder in a substantially non-agglomerated state by interposition. The method is characterized in that a mixed system consisting of a water-alcohol solvent containing complex ions, a hydrophilic polymer, a carbon powder, and fluorinated graphite is reduced by heating. As a result of various studies focusing on the hydrophobic properties of graphite fluoride, the present inventors discovered that graphite fluoride was further added to noble metal particles such as platinum particles and carbon powder when preparing an electrode catalyst for fuel cells. The degree of dispersion of platinum particles can be improved through interaction with coexisting carbon-based powder (carrier), and when forming an electrode plate, ideal three-phase The present invention was achieved by discovering that an electrode having an interface can be manufactured. The catalyst of the present invention is prepared by heating a mixed system consisting of a water-alcoholic solvent containing noble metal ions or noble metal complex ions, a hydrophilic polymer, carbon powder, and graphite fluoride at about 70°C for several hours (2 to 6 hours). time) prepared by heat treatment. At this time, by adjusting the blending amounts of each of the above-mentioned components, the noble metal particles are supported on the carbon-based powder in a substantially non-agglomerated state through the intervention of graphite fluoride. Note that, for example, the diameter of a platinum atom is about 5 Å, but in the present invention, the diameter of a platinum atom is about 10 to 5 Å.
Platinum particles with a diameter of 30 Å are considered as primary particles, and cases where there are approximately 10 or less of these primary particles are considered non-coagulated. The noble metals in the present invention include Pt, Pd,
Rh, Ru or Ir or mixtures thereof can be applied. Further, as the carbon-based powder serving as the catalyst carrier, graphite, carbon black (for example, acetylene black), activated carbon, or a mixture thereof can be used. As an electrode catalyst for fuel cells, the amount of noble metal supported is usually about 0.1 to 20% by weight, but from the relationship between the amount of precious metal per unit area of the electrode and cell performance, it is about 1 to 20% by weight.
The content is preferably 10% by weight. Further, the hydrophilic polymer in the present invention is used as a protective colloid, and PVA, polyvinyl methyl ether, polyvinyl pyrrolidone, polymethyl methacrylate, gelatin, gum arabic, etc. can be applied. Moreover, it is appropriate that the amount added is 0.1 to 50 in weight ratio to the noble metal. In addition, the amount of graphite fluoride added in the present invention is 10 to 10% based on the weight of the catalyst (noble metal particles + carbon powder).
A suitable content is 80% by weight. Furthermore, as the alcohol of the water-alcoholic solvent (and reducing agent) in the present invention, methanol, ethanol, isopropanol, 2-methoxyethanol, 1,2-dimethoxyethane, etc. can be used as appropriate, and the alcohol concentration teeth
A suitable range is 10 to 90% by volume. When supporting 1% by weight of platinum on an acetylene black carrier using 500ml of water-methanol (1:1) as a reducing agent, if a hydrophilic polymer such as PVA is not used, the number of platinum particles on the carrier may be several hundreds. ~several thousand Å
form coarse particles. When PVA is used, the primary particles of platinum become finer to 10 to 30 Å.
However, if the weight ratio (PVA/platinum) is less than 1/10, platinum particles will aggregate in groups of several dozen pieces and be dispersed and deposited on the carrier. When the weight ratio exceeds 20/1, platinum particles tend not to be deposited quantitatively on the carrier, and when the weight ratio exceeds 50/1, solid-liquid separation after catalyst preparation becomes extremely difficult. In addition, when the amount of platinum supported is 10% by weight, the amount of chloroplatinic acid used relative to the total amount of the reaction solution increases,
As a result of the lowering of the pH of the reaction solution, the action of the protective colloid is lowered, and at the same weight ratio (PVA/platinum) as the above-mentioned 1% by weight loading, the degree of dispersion of platinum particles becomes poor. Therefore, the reaction solution is neutralized with caustic alkali or carbonate alkali to keep the initial pH value constant (usually 1.5 to 1.5).
3.5), a predetermined amount of platinum particles can be deposited on the carrier regardless of the amount of chloroplatinic acid used. In the present invention, by adding fluorinated graphite particles during the preparation of the catalyst, it is possible to make the primary particles of the noble metal substantially non-aggregated. In other words, the addition of graphite fluoride gives a unique behavior between the carrier-colloid noble metal interaction,
Although the size of the primary particles of the precious metal deposited on the carrier does not change, the number of clusters of primary particles decreases from several tens when not added, and the degree of dispersion is significantly improved. In order to produce an electrode from the fuel cell electrode catalyst of the present invention, it is necessary to heat-treat the electrode catalyst. This heat treatment can thermally decompose the hydrophilic polymer of the protective colloid present on the surface of the noble metal particles and improve the catalyst performance. Heat treatment is performed at 100-400℃ under an oxidizing gas atmosphere, and at 100-500℃ under a reducing gas or inert gas atmosphere.
It is appropriate to carry out the reaction for about 2 hours, but it can be adjusted appropriately by repeating the oxidizing gas and the reducing gas alternately via an inert gas. For other steps, the electrode can be manufactured according to commonly used methods. Next, the present invention will be explained with reference to Examples, but the present invention is not limited to these in any way. Example 1 In a mixed solution of 250 ml of methanol and 225 ml of water,
1.0g of PVA was dissolved. To this was added 25 ml of chloroplatinic acid containing 20 mg of platinum per ml, followed by 5 g of acetylene black and 1.5 g of graphite fluoride. This was transferred to a round bottom flask equipped with a reflux condenser and heated to reflux at about 70° C. with vigorous stirring.
Within 4 to 6 hours after the start of the reaction, more than 99% of the initial amount of Pt was deposited on the acetylene black carrier. After filtering, washing with water, and drying, this electrode catalyst was observed using an electron microscope, and it was found that the primary particles of platinum were 10 to 30 mm in diameter.
Å, there were only a few colonies and they were uniformly dispersed on the carrier. Comparative Example 1 An electrode catalyst was prepared in the same manner as in Example 1 except that graphite fluoride was not added. The primary particles of Pt in this catalyst did not vary much in diameter, ranging from 10 to 30 Å, but the number of such particles was several dozen. Example 2 2.0 g of PVA was dissolved in a mixed solution of 250 ml of isopropyl alcohol and 100 ml of water. To this was added 100 ml of a chloroplatinic acid solution containing 20 mg of platinum per ml. Adjust the pH of this mixed solution to 2.2 with ammonia water.
The total volume was adjusted to 500 ml with distilled water. Then,
20 g of graphite and 2.0 g of fluorinated graphite were added to this solution.
Transfer this to a round bottom flask equipped with a reflux condenser,
The mixture was heated to reflux at approximately 70° C. with vigorous stirring. Within 4 to 6 hours after the start of the reaction, more than 95% of the initial amount of platinum was deposited on the graphite support, forming an electrode catalyst. After filtering, washing with water, and drying, this electrode catalyst was observed using an electron microscope, and it was found that the platinum particles had a diameter of 30 to 50 Å and were uniformly dispersed on the carrier. Example 3 In a mixed solution of 100 ml of methanol and 375 ml of water,
1.0g of PVA was dissolved. To this was added 25 ml of a chloroplatinic acid solution containing 20 mg of platinum per ml, followed by 5 g of acetylene black and 2.0 g of graphite fluoride. This was transferred to a round bottom flask equipped with a reflux condenser and heated to reflux at about 70° C. while stirring vigorously. Within 4 to 6 hours after the start of the reaction, more than 99% of the initial amount of platinum was deposited on the acetylene black carrier, forming an electrocatalyst. After filtering, washing with water, and drying this electrode catalyst,
When observed using an electron micrograph, the primary platinum particles had a diameter of 10 to 30 Å, and there were only a few clusters of them, which were uniformly dispersed on the carrier. Comparative Example 2 An electrode catalyst was prepared in the same manner as in Example 3 except that graphite fluoride was not added. The primary platinum particles of this catalyst did not vary much in diameter, ranging from 10 to 30 Å, but the number of colonies was as large as several dozen. Example 4 The electrode catalysts obtained in Examples 1 and 3 were heat-treated at 400°C for 2 hours in a nitrogen gas stream, and then treated with fluororesin (manufactured by Daikin Industries, Ltd.) to impart binding and water repellency properties. The suspension was added at a proportion of 10% by weight of fluororesin. After kneading this, it was applied to a carbon fiber sheet and then baked at 400° C. for 2 hours in a nitrogen stream to form an electrode. The amount of platinum deposited on each electrode was 0.45 mg/cm ² , and the performance of these electrodes as air electrodes was evaluated. The results obtained are shown in Table 1 below. In addition, as an electrolyte, 96%
H ₃ PO ₄ was used and the measurement temperature was 170°C.

[Table] As is clear from Table 1, the potential was 0.7 to 0.8 V at each current density, which was good. Example 5 The catalysts obtained in Examples 1 and 3 were placed in air,
After heat treatment at 300° C. for 2 hours, it was formed into an electrode plate in the same manner as in Example 4, and its performance as an air electrode was evaluated. The results obtained are shown in Table 2 below.

[Table] As is clear from Table 2, the potential was 0.7 to 0.8 V at each current density, which was good. Example 6 In this example, the electrode catalysts obtained in Example 1 and Comparative Example 1 and the electrode catalyst obtained in Comparative Example 1 were used, and graphite fluoride was added thereto when forming an electrode plate. The performance of each of the 7 pieces as air electrodes was evaluated, and the variations were investigated. The results obtained are shown in Table 3 below. In addition,
Tested at a current density of 100 mA/cm ² .

[Table] As is clear from Table 2, the electrode catalyst of the present invention has good performance and little variation. Furthermore, it has been found that no excellent effect can be obtained even when fluorinated graphite is added at the time of electrode formation. As explained above, according to the present invention, the noble metal particles of the noble metal (for example, Pt) catalyst can be made fine and uniformly dispersed and deposited on the carrier (carbon-based powder).
It is possible to improve the performance of fuel cell electrodes, and at the same time, because the fluorinated graphite as a water repellent agent is uniformly dispersed, it is possible to obtain the effect of stabilizing the performance of the formed electrode plate. can.

Claims (1)

[Scope of Claims] 1. Consists of noble metal element particles, carbon-based powder, and fluorinated graphite particles, and the noble metal element particles are supported on the carbon-based powder in a substantially non-agglomerated state through the presence of the fluorinated graphite particles. An electrode catalyst for fuel cells characterized by: 2. The fuel cell electrode catalyst according to claim 1, wherein the noble metal element is Pt, Pd, Rh, Ru, Ir, or a mixture of two or more thereof. 3. The fuel cell electrode catalyst according to claim 1 or 2, wherein the carbon-based powder is graphite, carbon black, activated carbon, or a mixture of two or more thereof. 4. The fuel cell electrode catalyst according to any one of claims 1 to 3, wherein the amount of the noble metal element is 0.1 to 20% by weight based on the weight of the carbon-based powder. 5. The fuel cell electrode catalyst according to claim 4, wherein the amount of the noble metal element is 1 to 10% by weight based on the weight of the carbon-based powder. 6. The fuel cell electrode catalyst according to any one of claims 1 to 5, wherein the amount of graphite fluoride is 10 to 80% by weight based on the total weight of the noble metal element and carbon-based powder. 7. A method for producing an electrode catalyst for a fuel cell, which comprises thermally reducing a mixed system consisting of a water-alcoholic solvent containing noble metal ions or complex ions of noble metals, a hydrophilic polymer, carbon-based powder, and graphite fluoride. . 8. The method for producing an electrode catalyst for a fuel cell according to claim 7, wherein the pH of the noble metal-water-solvent system is adjusted to about 1.5 to 3.5 before adding the carbon-based powder. 9. The method for producing an electrode catalyst for a fuel cell according to claim 7 or 8, wherein the noble metal element is Pt, Pd, Rh, Ru, Ir, or a mixture of two or more thereof. 10. The method for producing an electrode catalyst for a fuel cell according to any one of claims 7 to 9, wherein the carbon-based powder is graphite, carbon black, activated carbon, or a mixture of two or more thereof. 11. The method for producing an electrode catalyst for a fuel cell according to any one of claims 7 to 10, wherein the amount of the noble metal element is 0.1 to 20% by weight based on the weight of the carbon-based powder. 12. The method for producing a fuel cell electrode catalyst according to claim 11, wherein the amount of the noble metal element is 1 to 10% by weight based on the weight of the carbon-based powder. 13. Production of an electrode catalyst for a fuel cell according to any one of claims 7 to 12, wherein the amount of graphite fluoride is 10 to 80% by weight based on the total weight of the noble metal element and carbon-based powder. Method. 14 Alcohol is methanol, ethanol, isopropanol, 2-methoxyethanol or
1. The method for producing a fuel cell electrode catalyst according to any one of claims 7 to 13, which is 1,2-dimethoxyethane. 15 The alcohol concentration of the water-alcohol solvent is
The method for producing an electrode catalyst for a fuel cell according to any one of claims 7 to 14, wherein the content is 10 to 90% by volume. 16. Production of the fuel cell electrode catalyst according to any one of claims 7 to 15, wherein the hydrophilic polymer is polyvinyl alcohol, polyvinyl methyl ether, polyvinyl pyrrolidone, polymethyl methacrylate, gelatin, or gum arabic. Method. 17. The method for producing an electrode catalyst for a fuel cell according to any one of claims 7 to 16, wherein the hydrophilic polymer is blended in a weight ratio of 0.1 to 50 to the noble metal element.